Hybrid display

ABSTRACT

A hybrid pixel arrangement for a full-color display is provided, which includes an inorganic LED in at least one sub-pixel, and an organic emissive stack in at least one other sub-pixel. In an embodiment, a first sub-pixel is configured to emit a first color, and includes an inorganic LED, a second sub-pixel is configured to emit a second color, and includes a first portion of a first organic emissive stack configured to emit an initial color different from the first color. A third sub-pixel is configured to emit a third color different from the initial color, and includes a second portion of the first organic emissive stack, and a first color altering layer disposed in a stack with the second portion of the first organic emissive stack.

PARTIES TO A JOINT RESEARCH AGREEMENT

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a joint universitycorporation research agreement: Regents of the University of Michigan,Princeton University, University of Southern California, and theUniversal Display Corporation. The agreement was in effect on and beforethe date the claimed invention was made, and the claimed invention wasmade as a result of activities undertaken within the scope of theagreement.

FIELD OF THE INVENTION

The present invention relates to devices, such as full-color displays,which include both OLEDs and inorganic light emitting diodes or devices(LEDs), and other devices including the same.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting devices (OLEDs), organic phototransistors, organic photovoltaiccells, and organic photodetectors. For OLEDs, the organic materials mayhave performance advantages over conventional materials. For example,the wavelength at which an organic emissive layer emits light maygenerally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Color may be measured using CIE coordinates, which are wellknown to the art.

One example of a green emissive molecule is tris(2-phenylpyridine)iridium, denoted Ir(ppy)₃, which has the following structure:

In this, and later figures herein, we depict the dative bond fromnitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over” a second layer, the first layer is disposedfurther away from substrate. There may be other layers between the firstand second layer, unless it is specified that the first layer is “incontact with” the second layer. For example, a cathode may be describedas “disposed over” an anode, even though there are various organiclayers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed thatthe ligand directly contributes to the photoactive properties of anemissive material. A ligand may be referred to as “ancillary” when it isbelieved that the ligand does not contribute to the photoactiveproperties of an emissive material, although an ancillary ligand mayalter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative). Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled inthe art, a first work function is “greater than” or “higher than” asecond work function if the first work function has a higher absolutevalue. Because work functions are generally measured as negative numbersrelative to vacuum level, this means that a “higher” work function ismore negative. On a conventional energy level diagram, with the vacuumlevel at the top, a “higher” work function is illustrated as furtheraway from the vacuum level in the downward direction. Thus, thedefinitions of HOMO and LUMO energy levels follow a different conventionthan work functions.

Layers, materials, regions, and devices may be described herein inreference to the color of light they emit. In general, as used herein,an emissive component that is described as producing a specific color oflight may include one or more emissive layers disposed over each otherin a stack.

As used herein, a “red” layer, material, region, or device refers to onethat emits light in the range of about 580-700 nm; a “green” layer,material, region, or device refers to one that has an emission spectrumwith a peak wavelength in the range of about 500-600 nm; a “blue” layer,material, or device refers to one that has an emission spectrum with apeak wavelength in the range of about 400-500 nm; and a “yellow” layer,material, region, or device refers to one that has an emission spectrumwith a peak wavelength in the range of about 540-600 nm. In somearrangements, separate regions, layers, materials, regions, or devicesmay provide separate “deep blue” and a “light blue” light. As usedherein, in arrangements that provide separate “light blue” and “deepblue”, the “deep blue” component refers to one having a peak emissionwavelength that is at least about 4 nm less than the peak emissionwavelength of the “light blue” component. Typically, a “light blue”component has a peak emission wavelength in the range of about 465-500nm, and a “deep blue” component has a peak emission wavelength in therange of about 400-470 nm, though these ranges may vary for someconfigurations. Similarly, a color altering layer refers to a layer thatconverts or modifies another color of light to light having a wavelengthas specified for that color. For example, a “red” color filter refers toa filter that results in light having a wavelength in the range of about580-700 nm. In general there are two classes of color altering layers:color filters that modify a spectrum by removing unwanted wavelengths oflight, and color changing layers that convert photons of higher energyto lower energy.

More details on OLEDs, and the definitions described above, can be foundin U.S. Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

SUMMARY OF THE INVENTION

According to an embodiment, a pixel arrangement comprises a firstsub-pixel configured to emit a first color, the first sub-pixelcomprising an inorganic light-emitting diode (LED), which may be amicro-LED; a second sub-pixel configured to emit a second color, thesecond sub-pixel comprising a first portion of a first organic emissivestack configured to emit an initial color different from the firstcolor; and a third sub-pixel configured to emit a third color differentfrom the initial color. The third sub-pixel may include a second portionof the first organic emissive stack and a first color altering layerdisposed in a stack with the second portion of the first organicemissive stack. The second color may be the initial color, such asyellow. The first color may be blue.

The first organic emissive stack may include a single organic emissivelayer, or may include multiple organic emissive layers. Each layer mayinclude one or more emissive materials that emits light of the same ordifferent colors. The arrangement may include LEDs of only the firstcolor. The first sub-pixel may include a plurality of LEDs configured toemit the first color, which may be connected in series, parallel, orcombinations thereof.

The LED may be disposed in a stack with a third portion of the firstorganic emissive stack, such as where the organic emissive stack is anunpatterned stack.

The arrangement may include a fourth sub-pixel configured to emit afourth color different from the initial color, where the fourthsub-pixel includes a third portion of the first organic emissive stack;and a second color altering layer disposed in a stack with the thirdportion of the first organic emissive stack.

The pixel arrangement may include a plurality of pixels, each of whichincludes sub-pixels of at least three colors, at least four colors, ormore. Each sub-pixel containing one or more LEDs may be a sub-pixel ofat least two of the plurality of pixels, i.e., the sub-pixel may beshared among multiple pixels. The resolution of sub-pixels containingthe LEDs in the arrangement may be less than the pixel resolution of thearrangement.

The arrangement may include one or more backplanes, each of which may bepassive- or active-matrix. A first backplane may be configured to drivethe first sub-pixel, and/or each of the second and third sub-pixels, ora second backplane may be configured to drive each of the second andthird sub-pixels.

The first sub-pixel may be disposed on a first substrate, and each ofthe second and third sub-pixels on a second substrate. The firstsubstrate may provide a protective lid for each of the second and thirdsub-pixels. One or both of the substrates may be transparent and/orflexible.

At least one of the first sub-pixel and the second sub-pixels mayinclude a top-emitting OLED or a bottom-emitting OLED that includes thefirst portion of the first organic emissive stack.

In an embodiment, a pixel arrangement for a light emitting deviceincludes a first sub-pixel configured to emit a first color, whichincludes a plurality of inorganic LEDs electrically connected to oneanother in parallel; and a second sub-pixel configured to emit a secondcolor, different from the first color, which includes an OLED.

In an embodiment, a lighting device includes a plurality of blueinorganic LEDs disposed in a region that defines a first plane; and anunpatterned yellow organic emissive stack disposed in a second planeparallel to the first plane. The yellow organic emissive stack may betransparent, and blue light generated by the inorganic LEDs may betransmitted through the yellow organic emissive stack during operationof the device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIG. 3 shows a cross-sectional view of an example hybrid display in atop emission configuration as disclosed herein.

FIG. 4 shows an example schematic pixel arrangement according to anembodiment disclosed herein.

FIG. 5 shows an example of power consumption for a conventional display,and for various hybrid displays as disclosed herein.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporatedby reference in their entireties. Phosphorescence is described in moredetail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporatedby reference.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, a cathode 160, and a barrier layer 170.Cathode 160 is a compound cathode having a first conductive layer 162and a second conductive layer 164. Device 100 may be fabricated bydepositing the layers described, in order. The properties and functionsof these various layers, as well as example materials, are described inmore detail in U.S. Pat. No. 7,279,704 at cols. 6-10, which areincorporated by reference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MTDATA dopedwith F₄-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No. 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in U.S. Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. Pat. No. 7,431,968, which is incorporated by reference in itsentirety. Other suitable deposition methods include spin coating andother solution based processes. Solution based processes are preferablycarried out in nitrogen or an inert atmosphere. For the other layers,preferred methods include thermal evaporation. Preferred patterningmethods include deposition through a mask, cold welding such asdescribed in U.S. Pat. Nos. 6,294,398 and 6,468,819, which areincorporated by reference in their entireties, and patterning associatedwith some of the deposition methods such as ink-jet and OVJD. Othermethods may also be used. The materials to be deposited may be modifiedto make them compatible with a particular deposition method. Forexample, substituents such as alkyl and aryl groups, branched orunbranched, and preferably containing at least 3 carbons, may be used insmall molecules to enhance their ability to undergo solution processing.Substituents having 20 carbons or more may be used, and 3-20 carbons isa preferred range. Materials with asymmetric structures may have bettersolution processibility than those having symmetric structures, becauseasymmetric materials may have a lower tendency to recrystallize.Dendrimer substituents may be used to enhance the ability of smallmolecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the presentinvention may further optionally comprise a barrier layer. One purposeof the barrier layer is to protect the electrodes and organic layersfrom damaging exposure to harmful species in the environment includingmoisture, vapor and/or gases, etc. The barrier layer may be depositedover, under or next to a substrate, an electrode, or over any otherparts of a device including an edge. The barrier layer may comprise asingle layer, or multiple layers. The barrier layer may be formed byvarious known chemical vapor deposition techniques and may includecompositions having a single phase as well as compositions havingmultiple phases. Any suitable material or combination of materials maybe used for the barrier layer. The barrier layer may incorporate aninorganic or an organic compound or both. The preferred barrier layercomprises a mixture of a polymeric material and a non-polymeric materialas described in U.S. Pat. No. 7,968,146, PCT Pat. Application Nos.PCT/US2007/023098 and PCT/US2009/042829, which are herein incorporatedby reference in their entireties. To be considered a “mixture”, theaforesaid polymeric and non-polymeric materials comprising the barrierlayer should be deposited under the same reaction conditions and/or atthe same time. The weight ratio of polymeric to non-polymeric materialmay be in the range of 95:5 to 5:95. The polymeric material and thenon-polymeric material may be created from the same precursor material.In one example, the mixture of a polymeric material and a non-polymericmaterial consists essentially of polymeric silicon and inorganicsilicon.

Devices fabricated in accordance with embodiments of the invention canbe incorporated into a wide variety of electronic component modules (orunits) that can be incorporated into a variety of electronic products orintermediate components. Examples of such electronic products orintermediate components include display screens, lighting devices suchas discrete light source devices or lighting panels, etc. that can beutilized by the end-user product manufacturers. Such electroniccomponent modules can optionally include the driving electronics and/orpower source(s). Devices fabricated in accordance with embodiments ofthe invention can be incorporated into a wide variety of consumerproducts that have one or more of the electronic component modules (orunits) incorporated therein. Such consumer products would include anykind of products that include one or more light source(s) and/or one ormore of some type of visual displays. Some examples of such consumerproducts include flat panel displays, computer monitors, medicalmonitors, televisions, billboards, lights for interior or exteriorillumination and/or signaling, heads-up displays, fully or partiallytransparent displays, flexible displays, laser printers, telephones,cell phones, tablets, phablets, personal digital assistants (PDAs),laptop computers, digital cameras, camcorders, viewfinders,micro-displays, 3-D displays, vehicles, a large area wall, theater orstadium screen, or a sign. Various control mechanisms may be used tocontrol devices fabricated in accordance with the present invention,including passive matrix and active matrix. Many of the devices areintended for use in a temperature range comfortable to humans, such as18 C to 30 C, and more preferably at room temperature (20-25 C), butcould be used outside this temperature range, for example, from −40 C to80 C.

When used in a device such as a display, it may be convenient to referto an emissive stack of an OLED, in comparison to or in conjunction witha pixel or sub-pixel of the device. For example, an OLED stack may beused as the component that generates the initial light that ultimatelywill be emitted by a pixel or a sub-pixel. Generally, a “sub-pixel” is asmallest addressable emissive region in a device such as a full-colordisplay. A “pixel” generally includes multiple sub-pixels such that,during operation of a display, some or all sub-pixels within the pixelare driven to produce one overall resultant color. In some cases, eachpixel may be a “full-color pixel,” that is, one that includes sub-pixelsof each primary color of a particular rendering scheme (such asred/green/blue, red/green/blue/yellow, or the like), which can betreated as the smallest addressable imaging element, and generally iscapable of producing white light. In another type of configuration,individual sub-pixels may be included in rendering calculations usingtechniques typically referred to as sub-pixel rendering. Such techniquesmay require more extensive analysis and processing time, but may producesuperior images in some cases. Sub-pixel rendering typically usesinformation about the particular pixel and sub-pixel geometry of adisplay to manipulate sub-pixels separately, thereby producing anincrease in the apparent resolution of color displays. In such a device,each “pixel” within the display may not be identical to each other pixelwithin the same display, since each pixel may include differentsub-pixel colors and/or geometries. Regardless of whether full-colorpixels or sub-pixel rendering configurations and techniques are used, anindividual sub-pixel may be distinguished from OLED stack containedwithin the sub-pixel as disclosed herein.

A sub-pixel may include, or may be used in conjunction with, one or morecolor altering layers that alter the initial light generated by an OLEDstack in the sub-pixel. For example, a pixel may include red, green, andblue sub-pixels. The green sub-pixel may include a yellow OLED coupledto a green color altering layer, i.e., one that alters the initialyellow light generated by the OLED to green light that is ultimatelyemitted by the sub-pixel.

Within the OLED, an emissive stack generates the initial light, asdisclosed with respect to the emissive layers (EMLs) shown in FIGS. 1-2.An emissive stack may include one or more emissive layers, as disclosedwith respect to FIGS. 1-2. In some configurations an emissive stack mayinclude multiple individual layers of the same or different colors, or amixed layer that generates more than one color. Thus, each layer may bedescribed as generating its respective color of light, while the stackas a whole may be described as generating the same or a different colorof light than some or all of the emissive layers within the stack.

In some configurations, an “emissive stack” may include emissivematerials that emit light of multiple colors. For example, a yellowemissive stack may include multiple materials that emit red and greenlight when each material is used in an OLED device alone. When used in ayellow device, the individual materials typically are not arranged suchthat they can be individually activated or addressed. That is, the“yellow” OLED stack containing the materials cannot be driven to producered, green, or yellow light; rather, the stack can be driven as a wholeto produce yellow light. Such a configuration may be referred to as ayellow emissive stack even though, at the level of individual emitters,yellow light is not directly produced. Individual emissive materialsused in an emissive layer or stack (if more than one), may be placed inthe same emissive layer within the device, or in multiple emissivelayers within an OLED. As previously indicated, in some configurations,the final color emitted by an activated sub-pixel may be the same as thecolor provided by the emissive material in the stack that defines thesub-pixel, such as where a deep blue color altering layer is disposed ina stack with a light blue emissive stack to produce a deep bluesub-pixel. Similarly, the color provided by a sub-pixel may be differentthan the color provided by an emissive material in the stack thatdefines the sub-pixel, such as where a green color altering layer isdisposed in a stack with a yellow emissive stack to product a greensub-pixel. As used herein, the term “emissive stack” or “OLED stack”refers only to the layers necessary initially to generate light in anOLED arrangement as described with respect to FIGS. 1-2, such aselectrodes, emissive layers, transport layers, blocking layers, and thelike, and excludes color altering layers such as color filters, colorchange layers, and the like. It also excludes layers such as protectivefilms, single-layer barriers, and the like. As a specific example, asimple OLED stack includes an anode, a cathode, and a layer of organicemissive material disposed between the anode and the cathode. Acorresponding sub-pixel may include only the OLED stack, where thesub-pixel is intended to emit the same color of light as the lightgenerated by the organic emissive material, or it may also include acolor altering layer such as a color filter, when the sub-pixel isintended to emit a different color of light from that generated by theorganic emissive layer. An OLED stack also may include multiple layersthat could individually be considered separate OLED stacks, such aswhere one or more charge generation layers (CGLs) is disposed between ananode and a cathode, with a layer of organic emissive material disposedbetween the anode and the CGL, and a layer of another organic emissivematerial disposed between the cathode and the CGL. In such aconfiguration, the entire stack including the anode, cathode, CGL, andboth layers of organic emissive material may be considered a single OLEDstack. An OLED stack may be patterned or unpatterned, depending uponwhether the organic emissive layer or layers within the stack arepatterned or unpatterned at the pixel or sub-pixel level. That is, a“patterned OLED stack” is one in which one or more emissive layerswithin the stack have a pattern, such as a repeating arrangement ofregions of emissive material that are separated by another material. An“unpatterned OLED stack” refers to an OLED stack in which the relevantemissive layer or layers do not have such a pattern, such as, forexample, an emissive layer that is a uniform, continuous layer withinthe stack. Whether an OLED stack is considered patterned or unpatternedis determined only by the patterning or lack thereof of the emissivelayer or layers in the stack at a pixel or sub-pixel level, withoutregard to whether one or more electrodes or charge generation layerswithin the stack are patterned.

In some configurations, emissive layers and/or stacks may span multiplesub-pixels within the same device, such as where additional layers andcircuitry are fabricated to allow portions of an emissive layer or stackto be separately addressable.

An emissive stack as disclosed herein may be distinguished from anindividual emissive “layer” as typically referred to in the art and asused herein. In some cases, a single emissive stack may include multiplelayers, such as where a yellow emissive stack is fabricated bysequentially red and green emissive layers to form the yellow emissivestack. As previously described, when such layers occur in an emissivestack as disclosed herein, the layers are not individually addressable;rather, the layers are activated or driven concurrently to produce thedesired color of light for the emissive stack. In other configurations,an emissive stack may include a single emissive layer of a single color,or multiple emissive layers of the same color, in which case the colorof the emissive stack will be the same as, or in the same region of thespectrum as, the color of the emissive layer. In some cases a “stacked”device, i.e., one including multiple sets of layers that each could beconsidered a separate OLED device, may be arranged and controlled suchthat each individual stack within the overall stack may be separatelyaddressable. Such configurations are disclosed in further detail in U.S.Pat. Nos. 8,827,488 and 5,707,745, the disclosure of each of which isincorporated by reference in its entirety.

In contrast to OLEDs, inorganic or conventional light-emitting diodes(LEDs) have different advantages and disadvantages. For example LEDsoften may be operated at a higher luminance than OLEDs, and may be moreefficient at generating blue light, or can produce blue lightefficiently with a longer lifetime. However, OLEDs typically have agreater efficiency roll-off with increasing luminance, wider spectralline widths for similar emission colors, and may be used with a widerrange of substrates. Recent technical advances allow for micro-LEDs tobe fabricated efficiently and accurately placed at pre-determinedpositions on a substrate, making them suitable for use as sub-pixels inpixel-based devices such as full-color displays. As disclosed herein,combining micro-LEDs with OLEDs may allow for displays with improvedperformance and attributes compared to a similar device than uses eithertechnology independently. For example, many current OLED displayarrangements have fabrication issues related to patterning technologies,such as particulate and scaling issues when using fine metal masks fordeposition, or efficiency and lifetime issues when using white OLEDs inconjunction with color filters. As another example, current deep blueOLEDs may have unsatisfactory lifetime.

Micro-LED attachment is under ongoing development, but there are twosignificant issues in developing an all micro-LED display. First, thetypical yield for micro-LEDs may be insufficient to support full-colordisplay fabrication. Displays typically require near perfect sub-pixelyield, so any shorted or open micro-LEDs would be very problematic. Thesecond relates to the achievable grey scale of an all micro-LED display.Micro-LEDs, in particular green micro-LEDs, typically color shift asthey are dimmed, whether by analog or pulse width modulation drivingschemes, and red micro-LED color output is very temperature dependent.As a result, an all micro-LED display would be expected to haverelatively very poor color accuracy with grey scale. The only puremicro-LED displays currently in use are large-scale devices such asbillboards or video walls, which are not appreciably affected by theseissues.

As a result, it has been determined that a combination of micro-LEDs andemissive OLED stacks may provide an efficient and versatile hybriddisplay pixel arrangement. According to an embodiment, a hybrid pixelarrangement may include a first sub-pixel that emits a first color usingan inorganic LED. A second sub-pixel emitting a second, different color,may use an organic stack that generates an initial color. The secondsub-pixel may be unfiltered, i.e., it may ultimately emit the same coloras the light generated by the OLED stack, or it may include a coloraltering layer. A third sub-pixel may use the same emissive stack, andmay also use a color altering layer such that the sub-pixel emits adifferent color than either of the other sub-pixels. The LED may be amicro-LED, i.e., one having dimensions on the micrometer scale, such asa width of about 1-50 μm, which may be suitable for relatively smallapplications such as mobile devices, televisions, and the like. In someembodiments the LED may be larger, such as may be suitable for largerapplications such as signs and the like. A micro-LED may have variousshapes, including square, diamond, rectangular, or other shapes. As usedherein, an “LED” may refer to a micro-LED or a larger LED, asappropriate for the context or application in which the LED is used.

More specifically, as disclosed herein the use of blue LEDs with red andgreen OLEDs may provide a viable full-color display with relatively lowpower consumption and relatively high luminance, lifetime, yield, coloraccuracy and optical performance. As a specific example, as disclosedherein a combination of blue LEDs and yellow OLEDs may allow forrelatively simple and inexpensive fabrication while maintaining a highrange of color.

Further, the use of LEDs in conjunction with OLEDs allows for improvedphysical arrangements and fabrication techniques as disclosed herein.For example, an unpatterned yellow OLED may be placed over one or moreblue LEDs. Color filters can then be used to form green and redsub-pixels, resulting in a “RGBY” (red, green, blue, yellow) display.Preferred arrangements may share one blue LED amongst multiple pixels,typically four pixels, allowing for LED redundancy and LED placementresolution lower than the overall display resolution, in some cases halfthe display resolution or less, thereby overcoming or avoidingmanufacturing issues with accurate placement of the LEDs. Lowering theyield requirements for the LEDs through redundancy and the use of onlyone LED color may greatly ease manufacturability. The use of unpatternedOLED depositions, such as an unpatterned yellow stack, may allow for arelatively high fill factor and the potential to fabricate a stackedOLED architecture to further improve lifetime and display efficiency byreducing power consumption. Moreover, the relatively small areaallocated to the blue LED sub-pixel may allow for light and deep red andgreen sub-pixels enabling very high color saturation, without incurringhigher power requirements compared to a conventional OLED or LEDdisplay.

The OLED stack may include a single emissive layer, or it may be atandem or other stacked structure. The use of a tandem structure mayincrease the display lifetime by an approximate factor of three, andalso further decrease power consumption as described in further detailbelow. Stacking emissive layers of multiple colors is relativelydifficult to implement in a conventional RGB side by side displays, asit requires multiple deposition chambers and non-common layer OLEDstructures. According to embodiments disclosed herein, OLED stacks thatinclude multiple emissive layers may have yellow emissive materials inmultiple emissive layers or, for example, a red emissive material in onelayer and a green emissive material in another layer in the yellow OLEDstack. The advantage of using stacked red and green emissive layerswithin a common yellow OLED stack to render red, green, and yellowsub-pixels include a greater realized color gamut than in a similararrangement in which a single yellow emitter is used to render yellow.Alternatively or in addition, a yellow OLED stack may include yellow andred emissive layers. More generally, multiple emissive materials may beused in one or more emissive layers within an unpatterned emissive stackas disclosed herein.

In an embodiment, a hybrid display includes pixels having both inorganicLED and OLED sub-pixels. For example, a blue sub-pixel may be providedby one or more blue LEDs, and the remaining colors provided by one ormore OLED sub-pixels. As a more specific example, an unpatterned yellowOLED stack in conjunction with red and green color altering layers maybe used to provide red, green, and/or yellow sub-pixels. As used herein,a color altering layer refers to a structure such as a color filter,color altering layer, or color change layer, which alters the color oflight transmitted through the layer. Color altering layers do notgenerate initial light; rather, they merely alter the wavelength or peakwavelength of light that is incident on the layer as it is transmittedthrough the layer. As another example, red, green, and/or yellowsub-pixels may be patterned using OVJP, ink jet printing, LITI, or otherdirect patterning processes known for fabrication of OLEDs. Ifpatterning techniques are used, then red and green OLEDs may befabricated in a side by side architecture, allowing for a three-colorRGB hybrid display.

FIG. 3 shows a cross-sectional view of an example hybrid display in atop emission configuration as disclosed herein. Only one via is shownfrom the backplane to one OLED anode for illustration purposes, but itwill be understood that other similar arrangements may be used for otherOLED sub-pixels. As shown, an OLED sub-pixel 305 may be defined by anOLED anode 321, cathode 320, and a portion of an OLED stack 325. Moregenerally, one or more OLED sub-pixels may be defined across a region301 of a substrate 300, as described in further detail below. One ormore inorganic LED sub-pixels also may be defined in a separate region302. Although the example is shown using an unpatterned cathode 320above an individual sub-pixel anode 321, it will be understood thatother configurations, such as an unpatterned anode and individualcathodes, unpatterned layers separated by insulators or otherwisedivided into individual sub-pixels, or the like may be used.

As previously described, the OLED stack 325 may include one or moreemissive materials or layers, as well as other layers found inconventional OLED devices, such as those described with respect to FIGS.1-2. The OLED stack 325 may be an unpatterned stack that is disposed ina stack with areas of the pixel shown in FIG. 3 that correspond tomultiple sub-pixels. Multiple OLED sub-pixels may be defined by separateanodes, such as anode 321 that defines the sub-pixel 305. A coloraltering layer such as color filter 310 may be disposed in a stack withthe anode 321. Alternatively, the color altering layer 310 may beomitted, resulting in an “unfiltered” OLED sub-pixel that will emit thesame color of light as initially generated by the OLED stack 325.Sub-pixels that include a color altering layer 310 will emit a color oflight determined by the color altering layer 310, which will bedifferent than the color of light initially generated by the OLED stack325. Using the arrangement shown in FIG. 3, additional sub-pixels may becreated by placing additional anodes adjacent to the anode 321 and in aseparate stack from the anode 321, in a stack with a different portionof the OLED stack 325. For example, another anode placed adjacent to theanode 321 could be used to define an OLED sub-pixel that would emit thesame color of light as the light generated by the OLED stack 325,presuming no color altering layer was disposed in a stack with theadditional anode. If a second color altering layer was disposed in astack with the additional anode and the second portion of the OLED stack325, the additional sub-pixel would then emit light having the samecolor as light initially generated by the OLED stack 325.

As described in further detail herein, a TFT backplane 365 and otherassociated electrical structures may provide power to, and control of,the sub-pixels within a display via metal layers 340 disposed withinchannels 345 between the backplane 365 and the sub-pixels. Electricalconnections 355 from the LED 360 to the backplane 365 may provide powerand/or control of the LED 360.

A sub-pixel may include one or more inorganic LEDs 360. Typically nocolor altering layers are used in conjunction with the LED, so that thesub-pixel defined by the LED will emit the same color of light as thelight initially generated by the LED, although in some embodiments acolor altering layer may be used to modify the spectral output of theLED. As shown in FIG. 3, the organic stack 325 may be disposed over orotherwise in a stack with the micro-LED. This may not substantiallyaffect the color of light emitted by the LED sub-pixel, because theportion of the OLED stack 325 that is disposed in a stack with the LEDmay not be active and may not operate as a color altering layer withrespect to light emitted by the LED 360. For example, the OLED stack 325may be transparent, or substantially transparent with respect to thewavelength of light emitted by the LED 360. In some embodiments, theOLED stack may have a small impact on the color of the LED light passingthrough it even when the OLED stack may be considered transparent withrespect to the light emitted by the LED, as it may have a transmissionwhich varies with the wavelength of transmitted light.

The TFT 365 and associated circuitry may be formed on the substrate 300,which may be glass, metal or plastic. The substrate 300 may be flexibleand/or encapsulated. OLED anode contacts such as anode 321 may then beformed using any suitable technique, such as those known for use with aconventional OLED display, including those previously disclosed herein.

The TFT backplane may be fabricated on, for example, low temperatureplastics such as heat stabilized PEN, thus allowing for low temperaturebackplane technologies, such as OTFTs or oxide TFTs. Alternatively, theTFT be fabricated using LTPS on glass, polyimide or metal, or similartechniques.

Depending on the particular structure of the LED 360, the negativeelectrical connection to the LED may be provided by a common cathodealso used for the OLED devices such as cathode 320, and so may bepositioned above the LED devices as shown. Alternatively, the LEDcathode may be incorporated into the TFT backplane 365, in which caseunder each LED there would be two power connections such as connections355, with one being the conventional anode connection from the driveTFT, and the second being a common cathode connection that may beimplemented by a common cathode connection running parallel to the rowsor columns in the backplane in addition to providing a common cathodeconnection plane to the OLEDs. Such a configuration may be desirablebecause to connect a LED to the common OLED cathode may require a highfeature to break the organic film continuity, so that the conductingcathode connects to the top of the LED. An example technique toaccomplish such a configuration is for the thickness of a planarizationlayer 350 to be less than the height of the LED. More generally, theplanarization 350 may be used to planarize the different heightsresulting from use of a LED adjacent to and/or covered by an OLED stack325 as shown in FIG. 3. As another example, the electrical connections355 for the LED 360 may be disposed on the top surface of the die, inwhich case the die may be attached to the backplane 365 and then thedisplay planarized and vias 345 etched down to the backplane for allOLED and LED sub-pixels. The metalization 340 then may be deposited andpatterned to connect the backplane 365 to the OLED anodes 321 throughthe vias 345, and also from the backplane to the non-common LED topconnection. The LED common connections also may be connected by metallines patterned at the same time.

In embodiments disclosed herein, one or more LEDs may be fabricatedusing micro-printing, such as using systems available from X-Celeprint,electrostatic pick-and-place, such as using systems and techniquesavailable from Luxvue, or any other suitable technique. LEDs asdisclosed herein may be surface emitting, typically having a Lambertianemission profile, or edge emitting with a relatively narrower emissionprofile.

In some embodiments, an insulator may be disposed in a stack over theLED to prevent the OLED stack from being illuminated by it contactingthe LED anode connection or pad. For example, referring to theillustrative arrangement shown in FIG. 3, an insulator 335 may bedisposed over the LED 360.

In an embodiment, after the LEDs have been positioned and, if required,an insulator disposed over the LEDs, the substrate may be prepared forOLED deposition. Referring again to the example arrangement shown inFIG. 3, LED devices may have a height of about 0.5 to 10 μm, so aplanarization deposition 350, which may be transparent, may be appliedprior to OLED deposition. The planarization 350 may be organic orinorganic. In some cases, the curing temperature available for theplanarization may be limited by the choice of substrate and backplanetechnology. If the planarization layer would be expected to outgass andthereby degrade the lifetime of the OLED emissive stack, a permeationbarrier 330 may be deposited. The permeation barrier 330 may bedeposited after the planarization 350 instead of, for example, directdeposition over a plastic substrate. The thickness of the planarization350 may be less than LED height, equal to it, or slightly larger thanthe LED height. The vias 345 may be introduced with subsequentfabrication of metallization 340 as previously described, so as toprovide pads for OLED electrodes and electrical connection to the TFTbackplane.

Various pixel layouts may be used with embodiments disclosed herein. Insome cases, it may be preferred to use a layout with an unpatterned OLEDemissive stack at the pixel level. That is, an unpatterned layer orlayers may be deposited in a region to form the OLED stack, withoutusing a fine metal mask or other technique to deposit individual OLEDsub-pixels. Such a technique may avoid the complexities inherent in theuse of a fine metal mask for vacuum deposited OLEDs, or, similarly, inink jet and other patterning technologies for solution processed OLEDs.Alternatively or in addition, OLED sub-pixels may be deposited usingOVJP as previously disclosed herein.

In an embodiment, a full-color display may include multiple pixels, eachof which has a pixel arrangement as shown in FIG. 2, with multiple OLEDsub-pixels in each pixel. That is, the structure shown for sub-pixel 305may be repeated for other sub-pixels within each pixel. For example, ablue LED may be paired with two or three OLED sub-pixels having thebasic structure as shown for sub-pixel 305. As a specific example,green, red, and yellow OLED sub-pixels may be used, where each OLEDsub-pixel includes either an emissive stack that generates the samecolor as is ultimately emitted by the sub-pixel, i.e., green, red, andyellow OLED stacks, respectively. Alternatively, one or more OLEDsub-pixels may include an emissive stack that generates an initial colorof light that is then converted to the color emitted by the sub-pixel,as previously disclosed. Alternatively, two or more OLED sub-pixels mayshare a common OLED stack, with the sharing sub-pixels being defined byindividual electrodes, as previously disclosed. As a specific example, ayellow emissive stack may be used by red and green OLED sub-pixels, eachof which has a different color altering layer disposed in a stack with aseparate electrode to form the sub-pixel. In some embodiments, threeOLED sub-pixels may be used, such as red and green as previouslydescribed as well as an unfiltered (i.e., no color altering layer)yellow OLED sub-pixel. The use of such an RGBY architecture may providefor better efficiency and power usage than conventional RGB or RGBWarrangements. Generally, blue and yellow will be used to render imagesmost of the time, other than when very saturated green and red colorsare required. This allows for the display to have a high or wide colorgamut without a power consumption penalty.

In an embodiment, a further increase in color gamut may be achieved byusing a six-color display, such as a deep blue from LED and five OLEDsub-pixels, such as yellow, yellow, light green (550 nm-600 nm), deepgreen (500 nm-550 mnm), light red (580 nm-630 nm) and deep red (630nm-700 nm). In such a configuration, the deep green and deep redgenerally are only used a small percentage of the time, so theirrelatively lower efficiency will not significantly impact the overalldisplay power consumption. These very saturated colors may be achievedby applying color altering layers over portions of a yellow OLED stackas previously described, and further facilitated if the correspondingsub-pixels or corresponding portions of the emissive stack are placed inmicro-cavities. For example, portions of the yellow emissive stack maybe placed in microcavities to shift the spectral output to favor deepred or deep green as appropriate. Such an approach may be desirable, forexample, to achieve the full ITU-R Recommendation BT.2020 (“REC 2020”)color gamut.

In an embodiment, one or more LED sub-pixels may be shared among fourpixels. Such a configuration may reduce the required resolution andpositional accuracy requirements of placing the LEDs, and therebyincrease the manufacturing yield. In addition, the relatively large bluesub-pixels may allow for multiple LEDs to be positioned in eachsub-pixel, thereby providing redundancy without impacting the resolutionof the display, which also may greatly increase displaymanufacturability. As a specific example, each blue sub-pixel in a pixelmay include two blue LEDs arranged in parallel. Contact pads may beprovided for two independent LEDs in parallel, and connected to the samedriver TFT. As the driver TFT acts as a current source, the same currentwill flow in each blue sub-pixel whether both or only one LED isoperational, resulting in very similar light output. Such an arrangementthereby protects against failure of one of the LEDs without significantimpact to the display luminance or color gamut. Similarly, multiple LEDswithin a sub-pixel may be arranged in series to protect against shortingof the LEDs. Both arrangements may be used concurrently, such as wheretwo pairs of series LEDs are arranged in parallel, to providesimultaneous protection against damage, shorting, or other failure,without significant impact to the apparent operation ormanufacturability of the sub-pixel.

FIG. 4 shows an example schematic pixel arrangement according to anembodiment disclosed herein. As previously described, each pixel 401 inthe arrangement may include one or more blue sub-pixels 405, each ofwhich may include one or more inorganic LEDs 410. In the illustrativearrangement shown in FIG. 4, each blue emissive region, each of whichincludes two blue LEDs in the example, is shared among four sub-pixels,but other arrangements as previously described may be used in which eachblue emissive region is shared among a different number of pixels, or inwhich each pixel includes a separate blue LED, or in which the blueemissive region includes one or a different number of LEDs. Each pixelalso may include yellow, green, and/or red sub-pixels, each of which mayinclude an emissive OLED organic stack. As previously described, theOLED stack in each sub-pixel may be a portion of a unpatterned OLEDstack, such as where an unpatterned yellow organic stack is used inconjunction with red and green color altering layers to form sub-pixelsas shown. The use of an unpatterned OLED stack means that the sub-pixelfill factors may be determined by photolithography, such as by anodepatterning or the use of color altering layers. That is, although alarger-scale device as disclosed herein may include a “pattern” or maybe fabricated using patterning methods across the device as a whole, nopatterning of the organic films in the OLED stack or stacks within thedevice is required, such as at the level of individual pixels orsub-pixels. As a result, much higher fill factors can be achieved thanfor a conventional RGB patterned side by side OLED display that includesseparately patterned OLED emissive layers for each different coloredsub-pixel, or stacks of different colors. In addition, the bluesub-pixel may have the smallest fill-factor as previously disclosed, dueto relatively high lifetime and efficiency of blue LEDs. This in turnmay allow for a larger sub-pixel aperture ratio for the yellow or othersub-pixels, further increasing display lifetime, and/or allowing morespace to implement other architectures such as a six-color architecturefor very wide color gamut display as previously described. The use of anunpatterned organic stack also may improve the manufacturability of thedisplay, for example, by eliminating the need for patterning at thepixel level, and thus and otherwise allowing for lower manufacturingcosts than would otherwise be achievable.

Embodiments disclosed herein may use top and/or bottom emission OLEDs. Abasic OLED stack including the anode assembly may be optimized for ayellow OLED stack as previously described. Examples of variousarrangements and anode patterns that may be used with embodimentsdisclosed herein are provided in U.S. patent application Ser. No.14/698,352, filed Apr. 28, 2015, and published as US Pub. No.2015/0340410, the disclosure of which is incorporated by reference inits entirety. Color altering layers such as color filters may be used asdisclosed herein regardless of whether top- or bottom-emission OLEDstructures are used. For example, in bottom-emission structures, colorfilters may be patterned on the backplane, under the OLED stack, usingphotolithographic techniques. For top-emission structures, color filtersmay be patterned on a lid which is aligned and sealed to the substrate,such as lid 315 in FIG. 3

Because LEDs are relatively small on the scale of conventional OLEDsub-pixel devices, transparent hybrid displays as disclosed herein maybe fabricated using techniques similar to those used for conventionaltransparent OLED (TOLED) displays. Metal bus lines, TFTs and the LEDchip may limit the overall transparency of such a device. However, anunpatterned OLED stack as disclosed herein may be fabricated to betransparent without a color filter. For example, a transparent yellowOLED stack may be fabricated without a color filter.

Hybrid displays and pixel arrangements as disclosed herein may beflexible. For example, a plastic or barrier-coated plastic may be usedas a substrate, with flexible OTFT or oxide backplanes. As anotherexample, LTPS may be used. As shown in FIG. 3, the interface between therigid inorganic LEDs and the top of the TFT backplane may be a limitinginterface of a hybrid arrangement in terms of flexibility. Thus, for aflexible display, it may be preferable for the “neutral plane” to berelatively close to this interface. When a thin device is flexed, theneutral plane runs through the device and defines a plane which does notexpand or contract on flexing. Regions on one side of the neutral planeare in tensile stress, and regions on the other side are in compressivestress when the device is flexed. To avoid delamination or cracking ofmaterials, it may be desirable for a thin display to include stiff orinorganic materials close to the neutral plane. The neutral plane willbe in the middle of a symmetrical structure, and can be moved away fromthis position by materials having a large Young's modulus multiplied bytheir thickness, particularly if these films are placed away from themiddle of the device. In a hybrid display as disclosed herein, theinorganic LEDs generally will dominate the positioning of the neutralplane due to their thickness and rigidity. Thus, the neutral planetypically will lie approximately half way up the height of the LEDsassuming an otherwise symmetrical display structure. Thecurrent-carrying electrodes for the OLED stack also may have arelatively large Young's modulus, and so the position and thickness ofthese electrodes also may determine how the neutral plane is positionedwithin the device. Buslines placed under LEDs near the TFTs will tend topull the neutral plane down towards the substrate, and therefore near tothe micro LED to backplane interface. So a hybrid display as disclosedherein also may allow for all the current-carrying electrodes to bebelow the micro LEDs.

FIG. 5 shows an example of power consumption for a conventional RGBdisplay, a YB display implemented using only conventional OLED devices,a YB hybrid arrangement as disclosed herein with a single junctionyellow, and a hybrid arrangement as disclosed herein using a stacked(two device) yellow OLED stack. As shown, the YB hybrid may achievegreater than a 56% power savings over the conventional RGB OLED display.This increased efficiency may be realized through lower powerconsumption, a smaller power source, or a brighter display at the samepower consumption. Conventional OLED display luminance generally islimited by the shortest lifetime of a sub-pixel, typically the bluesub-pixel or sub-pixels. However, in a hybrid display architecture asdisclosed herein, the lifetime may increase by at least a factor of 10,20, 30, or more, thus allowing for operation at higher luminances anddaylight readability or HDR operation, with significantly reduced imagesticking. A conventional phosphorescent yellow OLED device typically hasan LT95 of about 50,000 hours at 3,000 cd/m². For a daylight readabledisplay operating at greater than 700 cd/m², the maximum yellowsub-pixel luminance would be about 8,000 cd/m², correspond to an LT95 ofabout 7,000 hours. Use of a stacked yellow OLED structure as disclosedherein may increase the lifetime by a factor of three or more, leadingto a display lifetime of over 20,000 hours at an operating displayluminance of 1000 cd/m² or more.

Various drive architectures may be used with embodiments disclosedherein. Grey scale for a conventional OLED display is enabled by analogcontrol of the OLED current by the drive TFT in the backplane circuit. Asimilar approach can be used for LEDs, although it may be difficult toachieve a high number of grey levels by just analog control, and pulsewidth modulation (PWM) is often employed as it allows for the LEDjunction temperature to remain constant and so reduce color shifts.Hybrid display arrangements as disclosed herein may be used with eitherdrive scheme. For example, using a typical TFT backplane with powerconstantly applied to the drive TFT and LED and/or OLED chain, PWM canbe implemented by running the display at a higher frame rate than thatrequired, and then use the sub-frames to achieve some form of digitalluminance control. For example, if the display is run at 480 Hz, butonly 60 Hz is required for the video signal, there can be 8 sub-framesper frame, allowing for 8 grey levels, which can be combined with analogcontrol. Examples of control schemes suitable for use with embodimentsdisclosed herein, including those having more than three colors ofsub-pixels, are provided in U.S. application Ser. No. 14/605,876, filedJan. 26, 2015, and published as U.S. Pub. No. 2015/0349034, thedisclosure of which is incorporated by reference in its entirety.

In an embodiment, only PL organic films may be used, and color alteringlayers may be used to convert blue light emitted by the LEDs to yellow,thus providing a device as disclosed herein that includes noactively-driven OLEDs. Blue LEDs thus may be used for each sub-pixel,each driven directly from TFT backplane. In such a configuration thedensity of LEDs may be higher, though they would only be of the singlecolor. The color altering layer also may be patterned to avoid downconversion of the blue to yellow in the blue sub-pixel.

In an embodiment production yield may be increased by testing thesubstrate after positioning the blue LEDs but prior to OLED deposition.Connecting the gate and data lines together may enable all bluesub-pixels in a device as disclosed herein to be energized, so that acamera could record LED yield prior to OLED deposition.

In an embodiment, LEDs and OLED stacks as disclosed herein may bedeposited on separate substrates. For example, the OLED stack may bedisposed on an active matrix substrate, with a top emissionconfiguration. The LED components may be patterned on a lid with colorfilters and driven in a passive matrix mode to avoid the cost andcomplexity of two backplanes. LEDs generally may be lower resolutionthan the OLED stack, and thus more suited to being driven with a passivematrix.

In an embodiment, a passive matrix arrangement may be used. This mayextend the usage range for PMOLED displays, as only the yellow OLED mayneed to be considered at high drive conditions, thus allowing for ahigher luminance and more row lines than would otherwise be achievable.This may lower the fabrication cost and complexity for small displays,and remove substrate temperature constraints. Such configurations may beused for display that require relatively high flexibility, such aswearable displays.

Embodiments disclosed herein may be particularly beneficial for digitalsignage, which typically has requirements for high luminance, lowresolution, and low frame rate. For example, a conventional large-scale(84-inch diagonal or larger) signage may operate at 2500 cd/m² with apower consumption of 2800 W. A hybrid arrangement as disclosed hereinmay not require a polarizer, and, assuming a 50% of efficiency for anactive-matrix OLED arrangement, may consume only 600 W for comparableluminance operation. For example, embodiments disclosed herein may beoperable to achieve 700 cd/m² or more, while drawing 10 mW/cm² or lessat a white point of the display. As used herein, a white point of adisplay refers to the white point correlated color temperature value ofthe display. White light emitted by a display as disclosed hereintypically defined with regard to its chromaticity coordinates in the CIE1931 XYZ color space chromaticity diagram. Often in display applicationsthe white point is described by a value such as D65, D50 or the like,which refers to white light having a correlated color temperature (CCT)of 6500 K (D65), 5000K (D50), and so on. Embodiments disclosed hereintypically may have a white point in the range of D50 to D90, though someembodiments may include a white point outside of this range. These CCTvalues correspond to white points on the blackbody curve, but inpractice white light will not be exactly on the blackbody curve, butclose to it, with some error in both the x and y co-ordinate. As usedherein, “white light” thus refers to a mixture of light from sub-pixelsthat produce a white light closest to the blackbody curve.

Embodiments disclosed herein also may be capable of operating at arelatively high luminance compared to conventional large-scale displaysand conventional OLED displays, such as 1000 cd/m², 2000 cd/m², or more.More generally, relatively high luminance may be achieved using a hybridarrangement as disclosed herein, while maintaining the benefits of anOLED display such as flexible substrates and curved displays.

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. The present invention asclaimed may therefore include variations from the particular examplesand preferred embodiments described herein, as will be apparent to oneof skill in the art. It is understood that various theories as to whythe invention works are not intended to be limiting.

We claim:
 1. A lighting device comprising: a substrate; a plurality ofblue inorganic LEDs disposed in a region that defines a first planeabove the substrate; and an unpatterned yellow organic emissive stackdisposed in a second plane parallel to the first plane and disposedabove the substrate and above or below the first plane relative to thesubstrate.
 2. The lighting device of claim 1, wherein the yellow organicemissive stack is transparent, and wherein blue light generated by theinorganic LEDs is transmitted through the yellow organic emissive stackduring operation of the device.
 3. The lighting device of claim 2,wherein the organic emissive stack is disposed over the plurality ofinorganic LEDs, and the plurality of inorganic LEDs are disposed withina planarization layer.
 4. The lighting device of claim 3, furthercomprising: a backplane disposed below the planarization layer; and oneor more metal layers electrically connecting the organic emissive stackto the backplane, the one or more metal layers extending through theplanarization layer.
 5. The lighting device of claim 4, wherein thebackplane further comprises one or more electrical connections, each ofwhich is in direct electrical communication with at least one of theplurality of inorganic LEDs.
 6. The lighting device of claim 3, furthercomprising a permeation barrier disposed between the planarization layerand the organic emissive stack.
 7. The lighting device of claim 3,further comprising an anode and a cathode disposed over theplanarization layer, wherein the organic emissive stack is disposedbetween the anode and the cathode.
 8. The lighting device of claim 1,wherein the lighting device is selected from the group consisting of: aflat panel display, a computer monitor, a medical monitor, a television,a billboard, a light for interior or exterior illumination and/orsignaling, a heads-up display, a fully or partially transparent display,a flexible display, a laser printer, a telephone, a cell phone, atablet, a phablet, a personal digital assistant (PDA), a laptopcomputer, a digital camera, a camcorder, a viewfinder, a micro-displayless than 2 inches diagonal, a 3-D display, a virtual reality oraugmented reality display, a vehicle, a video wall comprising multipledisplays tiled together, a theater or stadium screen, and a sign.
 9. Thelighting device of claim 8, wherein the organic emissive stack isdisposed over the plurality of inorganic LEDs, and the plurality ofinorganic LEDs are disposed within a planarization layer.
 10. Thelighting device of claim 9, further comprising: a backplane disposedbelow the planarization layer; and one or more metal layers electricallyconnecting the organic emissive stack to the backplane, the one or moremetal layers extending through the planarization layer.